Environ. Sci. Technol. 2007, 41, 4150-4157
Effects of Ethanol (E85) versus Gasoline Vehicles on Cancer and Mortality in the United States MARK Z. JACOBSON* Department of Civil and Environmental Engineering, Stanford University, Stanford, California 94305-4020
Ethanol use in vehicle fuel is increasing worldwide, but the potential cancer risk and ozone-related health consequences of a large-scale conversion from gasoline to ethanol have not been examined. Here, a nested globalthrough-urban air pollution/weather forecast model is combined with high-resolution future emission inventories, population data, and health effects data to examine the effect of converting from gasoline to E85 on cancer, mortality, and hospitalization in the United States as a whole and Los Angeles in particular. Under the base-case emission scenario derived, which accounted for projected improvements in gasoline and E85 vehicle emission controls, it was found that E85 (85% ethanol fuel, 15% gasoline) may increase ozone-related mortality, hospitalization, and asthma by about 9% in Los Angeles and 4% in the United States as a whole relative to 100% gasoline. Ozone increases in Los Angeles and the northeast were partially offset by decreases in the southeast. E85 also increased peroxyacetyl nitrate (PAN) in the U.S. but was estimated to cause little change in cancer risk. Due to its ozone effects, future E85 may be a greater overall public health risk than gasoline. However, because of the uncertainty in future emission regulations, it can be concluded with confidence only that E85 is unlikely to improve air quality over future gasoline vehicles. Unburned ethanol emissions from E85 may result in a global-scale source of acetaldehyde larger than that of direct emissions.
Introduction In 1826, Samuel Morey (1762-1843) patented the first internal combustion engine, which ran on ethanol and turpentine. Since then, ethanol fuel has been used in all industrialized countries. Today, ethanol is being promoted as a clean and renewable fuel that will reduce global warming, air pollution, and reliance on diminishing gasoline. These reasons have been used to justify subsidies and legislation encouraging ethanol use worldwide. Life-cycle assessments to date, though, suggest that corn ethanol’s effects on equivalent greenhouse gases emissions relative to gasoline are small, with an uncertain sign (1-8). Some of the same studies have hypothesized that ethanol from cellulose may result in lower net greenhouse-gas emissions than corn ethanol. To date, though, this hypothesis has not been tested on a large scale. With respect to air pollution, several studies have examined emission differences between gasoline- and ethanol* Phone: 650-723-6836; fax: 650-725-9720; e-mail: jacobson@ stanford.edu. 4150
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fueled vehicles (9-19). However, no study has examined the spatially varying effect on cancer or ozone-related illness throughout the United States that might result from a conversion to ethanol. Such a study is important because previous introductions of chemicals (e.g., tetraethyl lead, chlorofluorocarbons, DDT, dioxins) without an analysis led to damaging consequences. Air pollution (indoor plus outdoor) is also the seventh leading cause of death worldwide (20), so any change in fuel that could affect mortality should be examined prior to its implementation. Here, a 3-D atmospheric computer model that treats chemical and radiative transformations, meteorology, and transport, is used with 2020 spatially resolved emissions data to calculate spatially varying chemical concentrations from gasoline and ethanol. The ambient concentrations are then combined with health effects and population data to determine health risks due to the fuels. Results are analyzed at high resolution in Los Angeles and coarser resolution in the whole United States.
Methods The model used was the nested global-through-urban GATOR-GCMOM (21-25), described in the Supporting Information. For Los Angeles, three nested domains were treated: global (4°-SN × 5°-WE), California (0.2° × 0.15°), and Los Angeles (0.045° × 0.05°); for the U.S., two domains were treated: global and U.S. (0.5° × 0.75°). Los Angeles results are shown to test conclusions at higher resolution than in the U.S. Since Los Angeles has historically been the most polluted airshed in the U.S., the testbed for nearly all U.S. air pollution regulation, and home to about 6% of the U.S. population, it is also ideal for a more detailed study. Simulations were run comparing future (ca. 2020) fleets fueled by gasoline and E85, where E85 contains 85% ethanol and 15% gasoline. Since ethanol, itself, contains 5% gasoline as a denaturant, E85 is really 80% ethanol and 20% gasoline. E85 was examined since the large-scale replacement of gasoline would require a fuel with high ethanol content. 2020 was examined because flex-fuel cars replacing current gasoline vehicles, most of which cannot use E85, could substantially penetrate the U.S. vehicle fleet only by 2020. Future anthropogenic emission inventories for gasoline and E85 vehicles were prepared from the 2002 U.S. National Emission Inventory (NEI) (26), which treats spatially distributed point, area, and mobile onroad/nonroad emissions. Mobile emissions include evaporative and exhaust. Formaldehyde, acetaldehyde, and 1,3-butadiene result from combustion in gasoline and E85 but not from evaporation (10). Benzene and ethanol result from both. Non-NEI natural emissions were also treated (Supporting Information). The only emissions perturbed due to E85 were vehicle emissions since exposure in populated areas is affected far more by vehicle exhaust than production of ethanol or gasoline. Tables 1 and S4 (where “S” refers to Supporting Information) summarize the speciated 2020 “baseline” gasoline and “Case 1” E85 emission inventories used here for Los Angeles and the U.S., respectively. The 2020 gasoline inventory was prepared by reducing NEI evaporative and exhaust mobile gasoline and nongasoline emissions by 60%, which is consistent with two independent estimates. First, D. Streets (personal communication) derived speciated 2030:2000 emission factors by sector and world region assuming IPCC SRES A1B and B1 emission scenarios. Table S2 shows the result for the U.S. transportation sector and indicates that an across-the-board 60% mobile emission reduction for 2020 assumed here is conservative since it exceeds the 2030 10.1021/es062085v CCC: $37.00
2007 American Chemical Society Published on Web 04/18/2007
TABLE 1. Summed 2020 Baseline (with Gasoline Vehicles) and Sensitivity-Test (with E85 Replacing Gasoline in Onroad and Nonroad Vehicles) Emissions in the Los Angeles Model Domain (Slightly Larger than the SCAB)a
species carbon monoxide nitrogen oxides as NO2 organic gases methane ethane propane paraffin bond group ethene propene 1,3-butadiene olefin bond group methanol ethanol formaldehyde acetaldehyde higher aldehydes formic acid acetic acid acetone benzene toluene bond group xylene bond group isoprene bond group unreactive total organic gas (TOG) sulfur oxides as SO2 ammonia PM2.5 organic matter black carbon sulfate nitrate other total PM2.5 PM10 organic matter black carbon ulfate nitrate other total PM10
(1) 2020 baseline onroad gasoline (t/yr) 615,000 64,400
(2) 2020 baseline nonroad gasoline (t/yr) 168,000 45,400
(3) 2020 baseline total gasoline (t/yr)
(4) percent change from gasoline to E85
(5) Case 1 E85 replacing 2020 total gasoline (t/yr)
(6) 2020 baseline and E85 non-gasoline (t/yr)
782,000 68,900
+5 -30
821,000 43,200
285,000 189,000
8530 1220 465 44,720 3570 988 1390 949 0 0 650 232 3460 0 0 0 1270 6260 11,600 65 4540 89,883 473 7430
+43 0 -65 -80 -17 -65 -10 -17 0 b +60 +2000 -60 0 0 0 -79 -80 -80 -80 -80 +22 0 0
12200 1220 163 8940 2960 346 1250 787 0 69,800 1040 4650 1380 0 0 0 268 1250 2320 13 908 109,464 473 7430
198,000 17,200 4890 115,000 10,100 1680 718 2220 550 4720 2380 631 4080 139 246 2920 2550 26,800 12,400 134 28,600 448,000 22,700 28,900
6290 902 342 33,400 2660 739 1030 707 0 0 481 171 2590 0 0 0 951 4640 8570 48.6 3370 66,914 370 7410
2230 316 123 11,300 910 248 368 242 0 0 169 61.4 872 0 0 0 323 1620 3010 16.4 1160 22,969 103 20
724 242 41.3 1.8 265 1270
490 50 2.8 3.9 76.7 623
1210 292 44.1 5.7 342 1900
0 0 0 0 0 0
1210 292 44.1 5.7 342 1900
56,700 8330 3590 362 70,600 140,000
1230 412 70.2 3.0 450 2170
1140 116 6.5 9.1 178 1450
2370 528 76.7 12.2 629 3610
0 0 0 0 0 0
2370 528 76.7 12.2 629 3610
112,000 15,400 6330 856 298,000 433,000
a 2020 Baseline gasoline and nongasoline mobile emissions (onroad and nonroad) (Columns 1-3) were calculated as 40% of 2002 NEI emissions. Column 5 was then derived by applying Column 4 to Column 3. Column 6 includes point, fugitive, area, nonroad nongasoline, and onroad nongasoline emissions, which were held constant for both the gasoline and E85 simulations. Total emissions for the baseline gasoline simulation are the sum of Columns 3 and 6. Total emissions for the E85 Case 1 simulation is the sum of Columns 5 and 6. b Each “percent change from gasoline to E85” was estimated from Table 2, except that the ethanol emissions for E85 were calculated to ensure the TOG emissions from E85 divided by that from gasoline equaled 1.22 (a 22% increase, estimated conservatively from Table 2, row 1). Sensitivity test Cases 2 and 3 used the same emissions as Case 1, except that ethanol emissions were derived to ensure increases in TOG from E85 of 6% and 38%, respectively, instead of 22%. The 80% reductions of xylene and toluene were assumed since ethanol does not emit xylene or toluene but E85 contains 20% gasoline.
reductions in Table S2, interpolated to 2020, for most species. Second, Table S3 shows that the California Air Resources Board (CARB) estimates that total organic gas (TOG) emissions in the South Coast Air Basin (SCAB) may decrease 57.7% between 2002 and 2020, from 172 919 to 73 192 metric tonnes/ yr. Although the 60% reduction assumed here is consistent with CARB, the CARB estimate may be optimistic since it exceeds the 2020 reduction interpolated from Table S2. E85 vehicle emissions (Column 5) in Tables 1 and S4 were obtained by applying percent changes (Column 4) to baseline gasoline evaporative and exhaust emissions (Column 3). Ethanol emissions were then calculated as a residual (Table 1, footnote). In old E85 vehicles, only 5% of ethanol emissions are evaporative and the rest is exhaust (27), thus with new vehicles, ethanol emissions are closer to pure exhaust.
Percent changes in Table 1 were estimated from Table 2, which provides emission differences between E85 and gasoline or low ethanol/gasoline blends from measurements. E85 generally increased nonmethane organic gases (NMOG), methane, formaldehyde, and acetaldehyde and reduced 1,3butadiene, benzene, and nitrogen oxides. Carbon monoxide increased in half the studies. E85 increased acetaldehyde (1250-4340%) and formaldehyde (7-240%), two important ozone precursors. Table 3 compares 2002 NEI with 2002 CARB acetaldehyde emissions from mobile sources in Los Angeles. The NEI estimate was 36% lower (1050 versus 1630 tonnes/yr) than the CARB estimate. Table 3 also assumes 2020 acetaldehyde emissions to be 2000% of 2020 gasoline emissions, lower than the average emission difference of 2500% from six studies VOL. 41, NO. 11, 2007 / ENVIRONMENTAL SCIENCE & TECHNOLOGY
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TABLE 2. Measured Percentage Changes in Emissions of Gases or Groups of Gases from Vehicles or Engines Using E85 versus Gasoline or E5 (+ Indicates Higher E85 Emission)a D96 total organic gas (TOG) nonmethane org gas (NMOG) methane (CH4) formaldehyde (HCHO) acetaldehyde (CH3CHO) ethene (C2H4) butadiene (C4H6) benzene (C6H6) carbon monoxide (CO) NOx (as NO2) PM mass PM number
B98
N98
+15
+62 +48
+60 +3660
+228 +4340
N99
W01
L02
M02
S05
+38 +0
+43 +1440 -17 -85
+0 -62 +62 -34
+41 +3100
D06
G06
+17
+43 +31
+34 +11 +106
-33 -33
-4 -59
-38 +17
+95
+63 +240 +1430
M05
+340 +7 +1250
-13 -78 +32 +13
+31 +33
-23 -59
+320 -38 +31 +100
a D96 (9) Table 13, comparing gasoline and E85; B98 (10) comparing Limina RFG and Lumina E85; N98 (11) comparing flex-fuel vehicles with E85 and reformulated gasoline; N99 (12) comparing 1998 Taurus FFV with E85 and a 1998 Taurus gasoline vehicle; W01 (13) comparing conventional gasoline and E85; L02 (14) Section 3.4, summarizing E85 studies; M02 (15) comparing regular gasoline and E85 ethanol-regular blended gasoline under lean conditions - Tables 2 and 4 of that paper; S05 (16) average of three vehicles using E85 versus E5 at 22 °C under NEDC driving cycle; M05 (17) average differences between gasoline and E85 emissions from two vehicles (2005 Ford Taurus and 2005 Mercedes-Benz C 240), as determined by the California Air Resources Board on-road new vehicle and engine certification program, D06 (18) comparing gasoline and E85, G06 (19) Certification data comparison of gasoline and E85, averaged over emissions from four 2007 Chevrolet vehicles: Savanna, Avalanche, Suburban, Uplander.
TABLE 3. Comparison of Acetaldehyde Emissions (t/yr) from the California Air Resources Board Emission Inventory with Those from the U.S. National Emission Inventory for the Model Domain Used Here (Also Shown are 2020 Emission Estimates Assumed Here for a Gasoline Fleet and for an E85 Fleet) onroad gasoline or E85 2002 CARB SCABa 2002 CARB model domainb 2002 NEI model domainc 2020 NEI model domaind 2020 E85 model domaine
427 171 3420
onroad non-gasoline
total onroad
51.1 20.4 20.4
565 664 478 191 3440
nonroad gasoline or E85
154 61.4 1230
nonroad non-gasoline
total nonroad
total mobile
418 167 167
822 966 572 228 1397
1387 1630 1050 419 4837
a Reference 28. b The model domain is slightly larger than the SCAB. CARB emissions in the model domain were estimated by multiplying CARB emissions in the SCAB domain by 1.1756, the ratio of the populations of the model domain in 2000 (17,267,158) to that in the SCAB domain in 2000 (14,687,964) (Table 4). c 2002 NEI emissions for the model domain were obtained from the U.S. NEI (26). d 2020 emissions with a gasoline fleet were estimated as 40% of 2002 emissions. e 2020 E85 emissions were assumed to be 20 times those of onroad and nonroad gasoline emissions. E85 did not replace nongasoline emissions, which were held constant.
TABLE 4. Bottom-Up Calculation of Future Acetaldehyde Emissions from Onroad E85 Vehicles Replacing Gasoline Vehicles in the Model Domain A B C D E ) D × B/A F G)E × F × 365/109 H I)G×H J K)G×J L
2000 population in SCABa 2000 population in model domainb 2000 gasoline vehicle miles traveled per day in SCABc 2020 estimated gasoline vehicle miles traveled per day in SCABc 2020 estimated gasoline vehicle miles traveled per day in model domain 2020 estimated new-vehicle E85 acetaldehyde emissions (mg/mi)d 2020 estimated new-vehicle E85 acetaldehyde emissions (t/yr) 2002 ratio of fleet average to new-vehicle HC emissionse 2020 onroad gas acetaldehyde emissions at current fleet avg/new ratio (t/yr) 2020 estimated ratio of fleet average to new-vehicle HC emissions 2020 onroad gas acetaldehyde emissions at est. fleet avg/new ratio (t/yr) 2020 onroad gas acetaldehyde emissions here (t/yr)f
14,687,964 17,267,158 297,370,000 378,829,000 445,351,000 5-15 813-2438 10.4:1 8453-25,358 5:1 4065-12,195 3420
a Reference 29. b The model domain is slightly larger than the SCAB. Population in the model domain was determined from U.S. population data at 4 km resolution from the USEPA NEI population files (26) (e.g., Figure 2). c Reference 29. Gasoline vehicles were assumed to consist of passenger cars, light and medium-duty trucks 8500 lbs, urban buses, and school buses. d Estimate from studies in Table 2 and accounting for future improvements. e Determined from Figure 1. f Table 3.
in Table 2. Table 4 uses an independent, bottom-up approach to show that the 2020 acetaldehyde emission estimate for onroad gasoline vehicles (3420 tonnes/yr in Table 3) may be low, thus conservative. If future emission regulations reduce acetaldehyde from E85 more than estimated here, the impacts of E85 may be lower than found here, but since unburned ethanol may be a larger source of acetaldehyde than direct emissions, control of ethanol emissions would also be needed to have a large impact. 4152
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The Table 4 analysis assumes a 2020 fleet-averaged to new-vehicle emission ratio of 5:1. Figure 1 shows that the 2003 value was about 10.4:1. The ratio exceeds unity for the following reason: Since 1984, the U.S. 50 000-mile/5-year (half useful life) total hydrocarbon (THC) emission standard for light-duty vehicles (LDVs) has been 0.41 g/mi or stricter, and that for light-duty trucks (LDTs) has been 0.8 g/mi or stricter. Figure 1, though, shows that in 2003, pre-1993 modelyear LDVs and LDTs emitted >0.8 g/mi on average. Because
FIGURE 1. Vehicle-fleet-averaged hydrocarbon emission rate in 2003 (straight long-dashed line), determined from the frequency distribution of vehicle miles traveled versus vehicle age (30) and the hydrocarbon emission rate from several hundred thousand passenger vehicles and light-duty trucks in 2003 versus model year 1982-2004 (31). Emission rates prior to 1982 were held to the 1982 value. The ratio of the fleet-averaged emission rate (straight longdashed line) to the 2004 model-year emission rate (last point of solid line) is about 10.4:1. 1984-1992 vehicles emitted 35 ppbv ozone (ppbv) >50 ppbv pop (mil) expos. >35 ppbvj high ozone deaths/yr >35* med. ozone deaths/yr >35* low ozone deaths/yr >35* pop (mil) expos. >0 ppbvj med. ozone deaths/yr >0k ozone hospitalizations/yrk ozone ER visits/yrk PAN (ppbv)
4.78 3.00 0.195 0.480 33 50 48.5 49.5 56.3 19.826 1525 1320 509 21.220 4719 7060 8430 1.001
Case 1 E85 - gasc
Case 2 E85 - gasd
Case 3 E85 - gase
+0.0621 +0.0708 +0.0703 +0.701 +0.715 +0.709 -0.0158 -0.0131 -0.0131 -0.105 -0.104 -0.104 +0.315 +0.369 +0.424 -3.54 -3.52 -3.17 +1.38 +2.29 +0.291 +1.33 +2.27 +0.281 +0.785 +1.48 +0245 19.826 20.984 18.885 +140 +252 +28 +120 +218 +24 +47 +84 +9.4 21.220 21.220 21.220 +134 +223 +28 +645 +1170 +131 +770 +1390 +155 +0.0192 +0.0325 +0.0086
United States Case 4 E85 - gasf
Case 5 E85 - gasg
Case 1 w/E85b
Case 1 E85 - gasc
+0.0490 +0.658 -0.0147 -0.105 +0.221 -3.52 +1.08 +1.02 +0.600 19.507 +105 +91 +35 21.220 +105 +488 +582 +0.0037
+0.0792 3.93 +0.017 +0.753 2.16 +0.448 -0.0149 0.0819 -0.0072 -0.104 0.282 -0.0611 +0.481 392 +2.85 -3.29 466 -29.3 +1.48 33.6 +0.266 +1.45 42.2 +0.283 +0.949 53.3 +0.647 19.507 142.10 142.10 +150 5423 +213 +130 4720 +185 +50 1811 +71 21.220 340.78 340.78 +144 52,500 +416 +695 25,200 +988 +830 30,100 +1180 +0.0306 1.06 +0.0136
a Results are shown for the population-weighted 24 h averaged August near-surface mixing ratiosh of four human carcinogens (formaldehyde, acetaldehyde, 1,3-butadiene, and benzene); the resulting number of cancer cases and changes in the number of cancer cases based on USEPA CURES and OEHHA CURES; population-weighted 24 h averaged August ozone mixing ratios and differences in mixing ratios; deaths, hospitalizations, and emergency-room (ER) visits due to ozone and ozone differences; and 24 h averaged August PAN mixing ratios and differences in mixing ratios. b Case 1: w/E85: E85 simulation with emissions as in Table 1 (Los Angeles) and Table S4 (United States) (TOG-E85:TOG-gasoline ) 1.22 and NOx-E85:NOx-gasoline ) 0.7). c Case 1: E85 minus gasoline. E85 and gasoline emissions as in Tables 1 and S4. d Case 2: Same as Case 1, except NOx-E85:NOx-gasoline ) 0.55 instead of 0.70. e Case 3: Same as Case 1, except NOx-E85:NOx-gasoline ) 0.85 instead of 0.70. f Case 4: Same as Case 1, except TOG-E85:TOG-gasoline ) 1.06 instead of 1.22, with difference due to less ethanol emission. g Case 5: Same as Case 1, except TOG-E85:TOG-gasoline ) 1.38 instead of 1.22, with difference due to more ethanol emission. h A population-weighted mixing ratio is the monthly averaged mixing ratio in each near-surface grid cell of a model domain, multiplied by the population in that grid cell, with the result summed over all grid cells and divided by the total population of the domain (estimated as 21,220,474 for the Los Angeles domain and 340,779,223 for the U.S. domain in 2020). A population-weighted mixing ratio difference between the E85 and gasoline simulation is the difference in the monthly averaged population-weighted mixing ratio for each simulation. i USEPA and OEHHA cancers/yr are determined by summing the product of individual USEPA or OEHHA CUREs (cancer unit risk assessments, which are the increased 70-year cancer risk per µg/m3 sustained concentration change in a carcinogen) by the population-weighted mixing ratio or mixing ratio difference of a carcinogen and by air density, over all carcinogens, then dividing by 70 years. The simulation for February in Los Angeles confirms that mixing ratio changes of the carcinogens in February were similar to those in August. USEPA CURES are 1.3 × 10-5 for formaldehyde, 2.2 × 10-6 for acetaldehyde, 3.0 × 10-5 for butadiene, and 5.0 × 10-6 for benzene. The USEPA CURE for benzene ranges from 2.2 × 10-6 to 7.8 × 10-6. The average of these numbers was used. OEHHA CUREs are 6.0 × 10-6 for formaldehyde, 2.7 × 10-6 for acetaldehyde, 1.7 × 10-4 for butadiene, and 2.9 × 10-5 for benzene. j The population exposed to >35 ppbv was determined from the E85 simulation for each respective case. The population exposed to >0 ppbv was the entire population of the Los Angeles or U.S. model domain in 2020. k The high, medium, and low ozone death rates were estimated to increase by, respectively, 1.06, 0.917, and 0.354 per year per 100,000 population per 1 ppbv increase in 24 h average ozone above 35 ppbv; the hospitalization rate (medium case only) for ozone-related respiratory problems was estimated to increase by 4.91 per year per 100,000 population per 1 ppbv increase in 24 h average ozone; the emergency-room (ER) visit rate (medium case only) due to asthma associated with ozone was estimated to increase by 5.86 per year per 100,000 population per 1 ppbv increase in 24 h average ozone (Supporting Information). Deaths/yr, hospitalizations/yr, and ER visits/yr were obtained by multiplying ozone above 35 ppbv (for w/E85 columns) or change in ozone (for E85 - gas columns) in locations where ozone was above 35 ppbv by the health effect rates listed above and by the population (given in this table) exposed to 24 h average ozone mixing ratios above 35 ppbv in either Los Angeles or the U.S, as determined from the model) The results were then divided by two to account for months of the year when ozone is lower than in August. The simulation for February in Los Angeles confirms that health effects of ozone, while greater for E85 than gasoline in February, were small, supporting the division by two. The medium ozone deaths/yr >0 ppbv was calculated as the ozone >0 ppbv multiplied by the population exposed to >0 ppbv (both given in the table) and 0.917 deaths per 100,000 per ppbv, all divided by two to account for seasonal variation.
and monoterpene emissions were higher in the southeast than elsewhere (Figures S5.l and S5.m). Under such conditions, increases in ROGs have little impact on ozone but decreases in NOx decrease ozone, as found upon conversion to E85.
Discussion Here, the ozone health effects of E85 versus gasoline are examined. The relative risk of ozone mortality may increase above unity at about 35 ppbv (e.g., Figure 2 of 32), the cutoff assumed here for mortality, hospitalization, and asthma. Table 5 shows the population-weighted change in annual mortality, hospitalization, and ER visits due to E85 versus gasoline and E85 alone. In the 2020 Case 1 scenario, E85 was calculated to increase ozone-related mortality by 120 deaths/ yr (with a range of 47-140/yr) in Los Angeles and 185 deaths/ yr (72-216/yr) in the U.S. These death rates represent an increase of about 9% in Los Angeles and 4% in the U.S. over the projected death rates with gasoline vehicles. E85 also 4154
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increased hospitalization by about 650 and 990 in Los Angeles and the U.S., respectively, and asthma-related emergencyroom visits by about 770 and 1200 in Los Angeles and the U.S., respectively. Some increases in health risk in Los Angeles and the northeast were offset by decreases in the southeast, but the overall health risk was greater for E85 than gasoline. E85 health effects due to ozone significantly exceeded those due to cancer. Table 5 shows that, if ozone mortality effects occurred down to 0 ppbv rather than 35 ppbv in 2020, the change in mortality due to E85 would be about the same in Los Angeles as with the 35 ppbv threshold since most people in Los Angeles would already be exposed to >35 ppbv ozone. However, the change in the death rate in the U.S. with a 0 ppbv threshold would be about twice that with a 35 ppbv threshold. Whereas PAN has little effect on mortality, it is an eye irritant and damages crops. E85 increased populationweighted PAN in Los Angeles and the U.S. (Table 5). PAN
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FIGURE 3. Modeled differences in the August 24-hour average near-surace mixing ratios of (a) ethanol, (b) acetaldehyde, (c) formaldehyde, (d) 1,3-butadiene, (e) benzene, (f) ozone, and (g) PAN in Los Angeles and the United States when all gasoline vehicles (in 2020) were converted to E85 vehicles under the emission assumption in Tables 1 and S4, respectively. Figures S1 and S5 gives difference plots and E85-alone plots for additional chemicals for Los Angeles and the U.S., respectively. forms from NO2 and the peroxyacetyl radical (CH3CO3), which derives from acetaldehyde. E85 increased acetaldehyde and decreased NO2. PAN increased in Los Angeles and other highly populated areas (e.g., the northeast) where NOx remained high even after E85 reduced its levels (Figure 3f). PAN decreased in the southeast, where nitrogen NOx reductions due to E85 had a larger effect on it than elsewhere (Figure 3f). Four sensitivity tests were run for Los Angeles to examine whether the conclusions reached for the baseline case would hold if the E85/gasoline emission ratio differed, due to data uncertainty, from those in the baseline case. In the respective tests, E85 NOx was reduced 45% instead of 30% relative to gasoline (Case 2), E85 NOx was reduced 15% instead of 30% (Case 3), E85 TOGs were increased 6% instead of 22% (by decreasing unburned ethanol) (Case 4), and E85 TOGs were increased 38% instead of 22% (Case 5). In all tests (Table 5 and Figure S3), E85 increased ozone and PAN relative to gasoline. In Cases 2 and 4 ozone increases were greater than in Case 1; in Cases 3 and 5, they were lower. The results are consistent with expectations from an ozone isopleth (Figure S2). Another test was run to estimate the effect of converting the current, rather than 2020, Los Angeles vehicle fleet, from gasoline to E85. Although this would not be practical since most current gasoline vehicles cannot run on E85, such a test provides an upper bound of the possible effects of converting to E85. Under this scenario, baseline gasoline emissions were 150% higher than those in Table 1 (e.g., original 2002 NEI emissions were used). The percent changes in column 4 of Table 1 were then applied to 2002 NEI emissions to obtain E85 emissions. Figure S4 shows results from this test. It indicates that the peak differences (E85 minus gasoline) in daytime ozone and 24 h PAN were 275% and 500% higher than were those in the 2020 scenario (Figures S1.l and S1.m, respectively). Thus, ozone and PAN differences (E85 minus gasoline) increased superlinearly with increasing baseline emissions. One study (Table 2) found that E85 increased particle mass and number relative to E5. Here no difference in particle 4156
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emissions was assumed, to ensure a conservative result, and no effort was made to estimate the overall effect of E85 versus gasoline on particle exposure. However, E85 was found to increase sulfate (Figure S1.r) by increasing aldehydes, which increased OH (Figure S1.p), hastening sulfur dioxide oxidation (Figure S1.q). E85 also increased low-molecular-weight secondary organic mass (ethanol, acetaldehyde, and formaldehyde) dissolved in aerosol and fogwater, but it decreased nitrate (Figure S1.t) and high-molecular-weight secondary organic aerosol mass. In sum, due to its similar cancer risk but enhanced ozone health risk in the base emission case, a future fleet of E85 may cause a greater health risk than gasoline. However, because of the uncertainty in future emission regulations, E85 can only be concluded with confidence to cause at least as much damage as future gasoline vehicles. Because both gasoline and E85 emission controls are likely to improve, it is unclear whether one could provide significantly more emission reduction than the other. In the case of E85, unburned ethanol emissions may provide a regional and global source of acetaldehyde larger than that of direct emissions.
Acknowledgments I thank (alphabetically) Ken Caldeira, Mark Delucchi, Mike Dvorak, Diana Ginnebaugh, Christopher Green, Nathanael Greene, Roland Hwang, Coleman Jones, Dan Kammen, Jon Koomey, Gil Masters, Tad Patzek, Rich Plevin, and David Streets for helpful comments and suggestions. This work received partial support from NASA under grants NNG04GJ89G and NNG04GE93E.
Supporting Information Available Model description and emission data, and analysis of additional results. This material is available free of charge via the Internet at http://pubs.acs.org.
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Received for review August 31, 2006. Revised manuscript received February 19, 2007. Accepted March 14, 2007. ES062085V
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